Adjusting screws on carburetors are secured by means of an adjustment safeguard in order to prevent unauthorized adjustment of the idle adjusting screw or the main adjusting screw. The adjusting screws must however be adjustable in work apparatus having two-stroke engines in order to be able to adjust the optimal engine capacity in dependence upon the external operating conditions of the location of use such as the elevation above sea level. The quality of the exhaust gas must also be considered when adapting the adjustment in order to prevent an unnecessary burden to the environment.
U.S. Pat, No. 3,618,906 discloses an adjustment safeguard for an adjusting screw on a carburetor which includes a cap axially held in form-tight engagement. The cap is held on the head of the adjusting screw so that the cap cannot rotate relative to the screw. The cap includes a radial projection which coacts in the direction of rotation of the adjusting screw with a stop fixed to a housing. The cap is pressed onto the adjusting screw so that it cannot be lost after the carburetor is preadjusted. Accordingly, the user can only make an adjustment within the adjusting angle determined by the projection and the stop fixed to the housing. This adjusting possibility is so dimensioned that the exhaust gas quality is maintained which is necessary to keep the burden to the environment low.
The means for limiting the adjusting capability of the adjusting screw is, in practice, often removed from work apparatus especially for carburetors of two-stroke engines in order to adjust the motor capacity desired by the user without consideration as to the poor exhaust gas values. In the case of a check, the adjustment safeguards, which are most often removed by levering them off with a screwdriver, are again pressed into place so that the manipulations made are not easy to recognize visually.